1. Field of the Invention
The present invention relates to a dead battery preventing device and a dead battery prevention method and, more particularly, to a dead battery preventing device for preventing an engine start failure (a so-called dead battery) of a vehicle having an economy running function and a dead battery prevention method.
2. Description of the Relevant Art
Hitherto, in order to meet the requirement of conservation of natural resources, various kinds of techniques whereby fuel efficiency of a vehicle is improved have been proposed, and have been commercially practical. For example, there is a function (so-called economy running function) whereby an engine is automatically stopped when a vehicle stopped at an intersection or the like, and then, the engine is automatically started when a driver's foot was taken off a brake pedal, resulting in a reduction in fuel consumption during a stop.
When the speed is 0 km/h and the brake pedal is held down, it is judged that an engine automatic stop condition became satisfied and the engine is automatically stopped, leading to the economy running state (idle stop state). When the brake was released in the economy running state and therefore, an engine automatic start condition became satisfied, the engine is automatically started.
The vehicles having the above-described economy running function have problems specific thereto, and various kinds of techniques for solving the problems have been proposed. For example, the below-mentioned Patent Document 1 discloses a technique, wherein when a hood (bonnet) covering an engine is open in an economy running state, an event where the engine starts in the middle of an engine inspection or the like and a hand of a worker or the like gets caught in a rotating part of the engine can be avoided by prohibiting a starter of the engine from being activated (i.e. prohibiting a start of the engine).
The below-mentioned Patent Documents 2 and 3 disclose techniques, wherein when a big impact was given to a vehicle (e.g. a bump or opening/closing of a door occurred) in an economy running state, an event where an engine starts owing to a release of a brake without a driver's intention caused by the big impact, leading to a sudden start of the vehicle can be avoided by prohibiting a start of the engine.
Some of actually produced vehicles having the economy running function are manufactured in such a manner that an engine does not start even if the vehicle is shifted from an economy running state to an engine stall state and a brake is released when a hood was opened or a collision occurred in the economy running state, in order to secure safety.
Even if the vehicle is shifted from the economy running state to the engine stall state, a power supply to electrical components (such as an air conditioner) mounted on the vehicle is continued, similarly to the case of the economy running state. In either case of the economy running state and the engine stall state, the power supply to the electrical components mounted on the vehicle is conducted only with electric power from a battery since an alternator whose drive source is the engine does not generate power.
By the way, in the engine stall state, as described above, the engine does not start even if the driver's foot was taken off the brake pedal, and in order to restart the engine, the driver need turn an ignition key to a start position or push an engine switch. As a result, after the vehicle is shifted from the economy running state to the engine stall state, the driver might leave the vehicle in the engine stall state. For example, the driver might leave the vehicle without knowing that the vehicle is in the engine stall state.
In this case, if the engine stall state is long continued, there is a risk that electrical discharge of the battery may excessively progress, resulting in a dead battery (an engine start failure).
[Patent Document 1] Japanese Patent Application Laid-Open Publication No. 2004-251220
[Patent Document 2] Japanese Patent Application Laid-Open Publication No. 2003-138955
[Patent Document 3] Japanese Patent Application Laid-Open Publication No. 2004-143934